# Concepts and definitions

- Base index
In the base index the price of the calculation period is always compared with the base period. In the base index weights are usually changed less often than yearly, for example, at intervals of five years.

- Chain index
In the chain index the comparison takes place always between successive calculation periods. In the chain index the change in two calculation periods is used to take forward the index point figure of the desired base period. In the chain index the weights are changed in principle in each calculation period.

At times the chain index is also mentioned in such cases where the comparison period is retained fixed in comparisons within the year, but the comparison period and the weight structure of the index is changed whenever the year changes.

- Cost index
The cost index describes cost changes caused to entrepreneurs from acquisition of inputs for a contract or an assignment.

Costs are accrued by own labour input and various products and services bought. Cost indices are sometimes also referred to as input indices.

The cost index describes changes in prices of cost factors relative to the selected base year. Cost indices are calculated with a method where different cost factors are weighted together by their proportions of total costs. The Laspeyres calculation index formula is used in the calculation, whereby the weights are from the base year.

Statistics Finland produces cost indices for building construction and civil engineering, earth movers and forest machinery, rail, taxi and ambulance transport.

- Index
An index is a ratio describing the relative change in a variable (e.g. price, volume or value) compared to a certain base period (e.g. one year). The index point figure for each point in time tells what percentage the given examined variable is of its respective value or volume at the base point in time. The mean of the index point figures for the base period is 100.

- Index formula
Index formula is a mathematical function by means of which an individual key figure describing change is calculated from observation values (e.g. Fischer, Laspeyres and Paasche index formulas).

- Monthly change
Monthly change is the relative change in the index from a time period one month earlier. The change is usually expressed as a percentage.

- Point figure
Point figure is a change quantity used in price indices, which expresses the price, average price or index of the comparison period relative to the price, average price or index of the base period. The point figure of the base period is usually denoted by the number hundred. For example, if the point figure for a commodity at a certain point in time is 105.3, it means that the price of that commodity has risen by 5.3 per cent from the base period.

- Weight structure
Describes what meaning each sub-index (commodity, employee group, etc.) belonging to the index has for total index.

Official Statistics of Finland (OSF):
Cost index of civil engineering works [e-publication].

Helsinki: Statistics Finland [referred: 28.8.2016].

Access method: http://www.stat.fi/til/maku/kas_en.html

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